1. Field of Invention
The present invention relates to a method of welding, more particularly it relates to a method of welding which utilizes a metal electrode core encased within a pre-sintered ceramic insulating sleeve.
2. Description of the Prior Art
Although the present invention is discussed in terms of the preparation of three-dimensional compressor impellers, it should be understood that the present method is applicable to all welding situations which require that a strong and continuous weld, free of air pockets and slag deposits, be effected in physically confined areas.
Prior techniques for fabricating compressor impellers have involved the use of various casting methods; a problem, however, normally associated with these cast impellers is that they utilize a radial impeller blade which does not provide for maximum flexibility and optimum stage matching. Moreover, in use, radial impeller blade designs can accommodate only limited inlet velocity distributions, each having a single specific flow capability.
Many of the above-mentioned problems associated with radial impeller design blades have been overcome by the advent of impellers having the so-called three-dimensional design. These impellers utilize inlet blade angles which vary from the hub of the impeller to the shroud, allowing these type of blades to accommodate varying inlet velocity distributions, thereby providing improved performance over that of the conventional radial blade designed impellers. The three-dimensional design is also advantageous in that it can accommodate larger flows in closed impeller systems.
The new three-dimensional impeller design discussed above, however, requires a method of welding which can be accomplished through the narrow opening at the inlet and the outlet ports of the impeller. The desired welding process must therefore employ an electrode which not only is capable of being manipulated through the narrow openings but also be capable of providing a satisfactory weld deposit.
Welding techniques utilizing electrodes and specifically coated electrodes are well known in the art. The welding electrodes utilized in the past normally comprise a metal core rod or wire encased within a ceramic coating. As is known in the art, the coating may be effectuated by using a ceramic dipping technique. However, a problem which arises when utilizing the ceramic-dipped electrode is that the ceramic tends to flake during the actual welding process, adversely affecting the resulting weld deposit.
The present invention has overcome the problems encountered with the prior art welding processes by providing a welding electrode which is insulated using a pre-sintered ceramic sleeve. It has been found that the electrodes of the present invention resist chipping and spalling better than the prior art ceramic dipped electrodes, and therefore, produce a weld deposit free of contaminants and air pockets. Moreover, the use of a presintered ceramic sleeve provides a more uniform weld deposit and allows a more continuous welding without replacement of the metal core.
It is therefore an object of the present invention to provide a method of welding for the manufacture of a three-dimensional blade impeller design which gives maximum flexibility and optimum stage matching for a standard fabricated compressor line.
Another object of the present invention is to provide an improved welding electrode which gives a uniform and continuous weld deposit.
A further object of the present invention is to achieve the foregoing objects at substantial savings of material and labor, in both the coating and welding operation.
Still other objects and various further features of novelty and invention will become apparent from reading of the following specification in conjunction with the accompanying drawings.